Non-native goats and iguanas threaten Pacific islands

Green iguanas are displacing native species on islands Copyright: Vladimir Dinets/University of Miami/Bugwood.org

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[MANILA] Feral goats and green iguanas wreaking havoc with the ecosystems in the small islands in the Pacific, biologists warn, in two separate studies published in Pacific Science last month, calling for control or elimination of these animals.

The animals have been introduced there by humans, but are now threatening the survival of native wildlife.

Feral goats rapidly deplete grazing lands, the first paper warns, while green iguanas threaten the local horticultural industry, according to the second study. Iguanas also reportedly cause car accidents when they cross roads and motorists try to avoid them, it adds.


  • Feral goats can rapidly deplete grazing lands
  • Green iguanas are displacing native species and may harm local horticultural industries
  • It is vital to prevent these species from spreading further to other small islands

Both studies mention that invasive animals introduced to new habitats can carry diseases and parasites that native ones have no defence against.

Mark Chynoweth, a natural resource science manager at the University of Hawaii at Manoa and an author of the goat study, says that the population of feral goats on Pacific islands "poses a significant threat to the native flora and fauna, and is a critical barrier to conservation and habitat restoration".

"Non-native goats threaten native species through direct impacts — grazing — and indirect impacts, such as destruction of habitat," he adds.

The study recommends that the goats be removed from some of the vulnerable ecosystems in the Pacific.

Meanwhile, Wilfredo Falcón, a graduate student of the University of Puerto Rico and lead author of the second study, says that green iguanas have been imported to Pacific islands — both legally and illegally — from the Americas as exotic pets since the 1950s.

But because of the lack of natural predators on the islands and the iguanas’ high reproduction rate, their population has risen dramatically and they are now expanding their range and displacing local species, particularly in Fiji. Eradication can be difficult because of their camouflage.

"It is important for people to understand that exotic species may have negative impacts if they become established outside their native range," Falcón tells SciDev.Net. "Moreover, sometimes they can grow to unmanageable sizes — up to two feet in length — and they may become hard to deal with."

Randolph Thaman, a professor at the University of the South Pacific in Fiji, says: "Both goats and green iguanas clearly constitute serious threats to small islands and their fragile native and cultural biodiversity and ecosystems, with goats having historically proven to be particularly disastrous".

He suggests that management efforts for both species should focus on preventing them from spreading, especially to smaller uninhabited islands with indigenous local iguana populations and threatened island ecosystems that have highly endemic plants and animal communities.

"The message from these two well-researched papers is that, for small islands — especially those with important populations of native or endemic animals and productive polycultural agricultural systems that are a foundation for food and productive security — the prevention or eradication of invasive alien species and diseases, remains the most positive option," Thaman says.

Link to goat study

Link to iguana study

This article has been produced by SciDev.Net’s South-East Asia & Pacific desk.


Pacific Science doi: 10.2984/67.2.2 (2013)
Pacific Science doi: 10.2984/67.2.1 (2013)